I. nucleotides: sub units „³ DNA A. Phosphate group B. 5-carbon sugar
molecule (deoxyribose) C. nitrogen base 1. Adenine 2. Guanine 3. Thymine 4.

Cytosine Chargaff „³ base pairing rule: 1 = 3 and 2 = 4 II. Maurice Wilkins
and Rosalind Frankilin „³ X-ray diffraction photos of DNA molecule - DNA
molecules: tightly coiled helix and composed of two or three chains of
nucleotides III. Chargaff builds a model of the double helix: a spiral
staircase of 2 strands of nucleotides twisting around a central axis. A.
alternating sugar and phosphate units B. purine and pyrimidines paired up - A
can only form hydrogen bonds with T - C can only for with G. „³ 2 strands
that are complementary to each other IV. Copying of DNA: A. Replication: process
of synthesizing a new strand of DNA. B. Helices: open up the double helix by
breaking the hydrogen bonds that link the complementary bases. C. Two strands
separated: additional enzymes and proteins attach to the individual strands and
hold them apart „³ twisting prevented D. Replication fork : where double
helix separates 1. DNA polymerases: enzymes that move along each strand „³
adding nucleotides to the exposed bases. 2. Proofreading „³ one old and one
new DNA strand 8.3 The Structure of a Gene - genes hold info specifying how to
build particular proteins - affects the phenotype of an individual because of
the activity of the protein that it specifies - DNA encoded info that specifies
particular proteins; each gene is made of a specific sequence of nucleotides I.

Genes in Eukaryotes A. interruped by necleotides that have no coding info. 1.

Introns:: noncoding sequences/ intervening - must be removed 2. Exons
:nucleotide segments that code for amino acids -stitched together once all
introns are removed II. Multigene families: clusters of almost identical
sequences; cells exist in multiple copies A. Some are silent genes: don\'¦t make
protein B. Some are only active during embryonic or fetal development C.